The invention relates to a process and an apparatus for injection of a predetermined quantity of fluid into a body by means of a syringe operated by an actuating mechanism.
In many cases, the injection or withdrawal of fluids to and from tissue or blood vessels must take place at constant flow rate, i.e., independently of extraneous conditions such as the input resistance of the system, the viscosity of the fluid or the time limits imposed by the functioning of internal body organs.
Already known are syringes which are controlled by a single-action cylinder/piston actuator to which is admitted hydraulic pressure. The piston is returned by a spring, permitting refilling of the cylinder. However, the force exerted by this spring is proportional to its degree of compression and thus depends on the position of the piston. Because of the varying actuating pressure exerted on the piston, the known system cannot deliver a constant flow rate.